This invention relates to a push-pull switch for use in an electronic watch, and is more particularly directed to a switch of the type having an axially movable stem biased into a central position at which both of two sets of contacts of the switch are open, such switch being referred to hereinafter as a switch of the type described.
In a switch of the type described, wherein both sets of contacts are normally open, movement of the stem in one axial direction away from a central position to a first terminal position allows the stem to bridge one set of contacts, while movement in the opposite direction to a second terminal position allows the stem to bridge another set of contacts. Upon release of the stem when it is in either terminal position, a spring-bias returns the stem to its central or neutral position. A conventional switch of the type described achieves this result by employing a pair of springs, alternatively effective to resiliently resist axial movement of the stem in either direction away from its central positon. In this type of switch, the two springs are arranged serially along the axis of the stem, only one or the other being effective at any one time. This arrangement requires a relatively long package to contain the switch, a factor that makes it difficult to utilize a switch of this type in an electronic watch where size is of critical importance.
In another type of conventional switch of the type described, a double-sided conical cam mounted on the stem is engaged by a spring-loaded cam follower mounted for displacement in a direction perpendicular to the axis of the stem. Displacement of the stem in either direction causes the cam to compress the spring so that upon release of the stem, the cam follower exerts an axial force on the stem returning the same to its neutral position. One spring is used in this switch, but it extends radially from the axis of the stem causing the package to be irregularly shaped and unsuitable for use in an electronic watch.
It is therefore an object of the present invention to provide a new and improved switch of the type described in which a single spring is used for the purpose of biasing the spring to its central position, but the switch package is nevertheless small and compact as compared to the prior art devices.